Robots are known which have a plurality of arms which are mutually rotatable about two axes each. A first arm is rotatably mounted about a first axis (roll axis) relative to a base. On the first arm, a second arm is rotatably mounted about a second axis (pitch axis) which is perpendicular to the first axis. Further, the second arm is rotatable about a third axis (roll axis) perpendicular to the second axis. Finally, an outermost arm carries a tool holding fixture through which a tool can be connected to the arm. This outermost arm is likewise connected rotatably about a pitch axis to the next inner arm and, in addition thereto, rotatable about a roll axis. Known robots have, for example, six such axes (pitch and roll axes). The arms are moved by servomotors which operate about different axes. The servomotors are energized by suitable signals to position the tool.
For the exact positioning of a tool held in the tool holding fixture the joints between the arms have to execute exactly defined rotational movements about the various axes. Sources of errors result from inaccuracies of the angle pick-offs, by misalignments of the axes or by longitudinal errors of the arms, which can be due to manufacturing tolerances or thermal dilation. Therefore, it is necessary to calibrate the robot.
The robots can be measuring or assembling robots.
It is known to move the tool of the robot to determined known positions. These positions can be formed by surfaces of a calibration body. The errors can be mathematically determined from the deviations of the attained positions of the tool from the known "desired positions".
These known methods are only partly usable for a six-axis robot. The calibration is only valid for a limited spatial area. Not all of the essential error terms can be determined. the handling is very complicated.
It is the object of the invention to calibrate robots with as low expenditure as possible and with high accuracy.